Primary photochemistry of the reaction center of photosystem I.

The earliest primary photochemical reaction of green plant photosynthesis has, thus far, remained unexplored as reaction center chlorophyll a (Chl a) complexes have not yet been isolated [l] . In contrast, primary photochemical steps have been successfully studied, with picosecond (ps) absorption spectroscopy [2,3] in isolated bacteriochlorophyll (B Chl)-reaction center complexes from photosynthetic bacteria. Here, the primary charge separation occurs within 10 ps followed by electron transfer, within 200 ps, to a relatively stable (>l ms) acceptor (Q-Fe, a quinoneiron complex):